A sense amplifier is electronic circuitry that sometimes is included in a memory component in an electronic device to read the state of memory cells. Sense amplifiers commonly are used in memory cell arrays to sense the difference between a memory cell bit-line voltage/current and a reference cell bit-line voltage/current and to amplify the difference so as provide a rail-to-rail output voltage. This reading process depends on how much current a memory cell sinks under well-defined biasing conditions. The task of a sense amplifier is to transform this current information into binary information that is suitable to be used as internal digital memory data. In some cases, the binary information consists of two logical levels (“1” or “0”), which correspond, respectively, to the memory cell states in which the cell sinks or does not sink a current under well-defined biasing conditions.
One way to read the cell state is to compare the cell current (Icell) with a reference current (Iref), usually provided by another cell, and track the process characteristics of the memory cell. The reference cell usually sinks a current having a value placed between the cell current in the logical state “1” and the cell current in the logical state “0.” For example, if the memory cell in the state “0” sinks no current, the reference cell could sink one half of the cell current in the logical state “1.” The sense amplifier reads the difference between the cell current and the reference current, and transforms the difference into binary information suitable to be used by the other memory chip circuits. For example, the current difference can be positive or negative if the cell state is “1” or “0,” respectively, so that the sense amplifier generates a binary signal “1” or “0,” respectively.
Some sense amplifiers operate in two clock phases: an equalization phase and a sense-latch phase. In the equalization phase, the sense amplifier output is reset by equalizing the sense amplifier's differential outputs. During the sense-latch phase, the sense amplifier compares the two input voltages/currents and generates a differential output voltage corresponding to a logic ‘0’ and ‘1’.